This invention relates to the positioning of orthodontic appliances on the teeth of a patient, and more particularly, to the configuration of orthodontic appliances, particularly orthodontic brackets, for the visual positioning thereof on the teeth of patients.
When bonding orthodontic appliances, a major tenet to be considered by the orthodontist is the location of the appliance in the mouth of the patient. In the case of bonded orthodontic brackets, this location is the position and orientation of each of the brackets on one of the teeth of the patient.
Most of the preadjusted appliances that are currently employed for maxillary application are designed to be located at the facial axes of the maxillary teeth of the patient. The facial axis, or FA point of a tooth illustrated as Point FA in FIG. 1A, is defined as dead center vertically on the clinical facial surface of a fully erupted crown and at the height of contour mesiodistally of the mid-developmental lobe of the tooth, for example, right maxillary central 20. This definition is based on the criteria that the plane of the archwire will pass through the point FA. Furthermore, appliances should be aligned angularly in the FA plane, which is the plane tangent to surface of the tooth at the FA point, at a line angle represented by line LA in FIG. 1A. This angle LA generally coincides with the line along the height of the contour of the tooth""s mid-developmental lobe 21. So angularly aligned, the appliance will better deliver the appropriate final angular position or tip of the tooth. These criteria are referred to as the concept of morphological centering and angular alignment. This concept is quite often implemented visually by the orthodontist or other clinician who places the appliance on the tooth by making a visual determination of the location of the point FA and the orientation of the line LA. The visual implementation of this concept can be rendered difficult for the orthodontist by varying degrees of eruption that leaves an unerupted portion 22 of a tooth 20a, as illustrated in FIG. 1B, by virtue of chipped or worn incisal tooth edges 23 of a tooth 20b, as illustrated in FIG. 1C, or by virtue of the existence of other aberrations of the typical tooth profile. Teeth for mandibular application are also often visually placed in accordance with mandibular placement criteria.
While the concept of morphological centering and angular alignment is familiar to orthodontists, the clinical difficulty of achieving its placement goals is well known. Several approaches have been developed to alleviate this problem but all have drawbacks. The most common approach has been to use measuring instruments to position the appliances at fixed vertical heights. These heights typically represent something akin to the average distance from the incisal edge of a tooth to the FA point of the tooth, and are usually expressed in millimeters. The awkwardness of this approach is that teeth come in various sizes, which precludes placement of the appliance at the proportional center of the tooth in all but the truly average patient. Additionally, due to the highly probably presence of a malocclusion and to the lack of access because of the tooth""s position in the mouth (e.g. as with posterior segments or crowding) there is often insufficient space to use these instruments effectively.
When the appliances are not placed at the design location, adverse effects occur with respect to the final positioning of the teeth. First, if the appliance such as an upper right central bracket 24 is placed incorrectly in the vertical plane, the faciolingual inclination of the tooth is effected, producing an inclination error 25 as illustrated in FIG. 1D. Secondly, at the same time, the apparent thickness of the appliance is effected, resulting in a labial-lingual offset error 26 from the desired placement of a tooth on the dental arch.
Another approach to this problem is that known as xe2x80x9cindirect bonding.xe2x80x9d This approach involves positioning of the appliances on a model or cast of the patient and then using a transfer mechanism or tray to transfer the positioned appliances to corresponding positions on the teeth of the patient. The indirect bonding approach has its detracting features. For instance, often the tray does not seat fully, causing simultaneous incorrect placement of a multitude of individual appliances. Other problems include appliance adhesive failure and excessive xe2x80x9cflash.xe2x80x9d Further, brackets are typically, although not always, placed by eye on the model, which offers little improvement over direct placement on most patients. These difficulties have been sufficient to severely limit the use of the indirect bonding technique.
An understanding of why the centering and aligning of appliances has been so clinically troublesome can be obtained by examining the morphology of the appliances and the dentition. Teeth, as most anatomical entities, have a generally flowing shape which does not lend itself to description or visualization using geometric determinants, as can be seen from the profile of a typical upper right cuspid 40 in FIG. 1E. Appliances such as brackets and their bonding pads, on the other hand, are typically generated from orthogonal geometric designs that lend themselves to ease of appliance manufacture, as can be seen from a typical upper right cuspid bracket 42. Further complicating this situation with respect to vertical placement is the varying torque or inclination angle of the archwire slot relative to the base of the appliance. This occurs whether an angle of a slot is cut in a bracket support, i.e. xe2x80x9ctorque in the facexe2x80x9d, or an angle is formed in the mounting surface of a bracket, e.g., xe2x80x9ctorque in the basexe2x80x9d. Because of this angle, the true plane of the archwire, which should intersect the FA point, is difficult for the orthodontist to visualize. Thus, positioning of the appliance, such as with the illustrated high torque upper right central bracket 24a, using either the bracket body or the facial view of the slot, will yield the positioning of the bracket on a tooth, such as tooth 20, with the archwire plane AWP intersecting the tooth 20 at a point displaced from the point FA, by an amount 28, as illustrated in FIG. 1F. Such a view afforded the clinician when placing the appliances often incorrectly influences the positioning. For the clinician to attempt to minimize this problem by viewing directly into the slot of the appliance during placement is at least awkward and not always possible clinically.
Additionally, when placing the appliance mesiodistally, the geometric appearance of the bracket and bonding pad can also be misleading, as seen when the rhomboid geometry of some individual appliances is compared to the dental anatomy. For example, FIG. 1G illustrates the difference between the shapes of orthogonal upper right cuspid bracket 42 and the anatomical shape of the upper right cuspid 40 with the bracket 42 correctly placed on mid-developmental lobe 41 that is not coincident with the mesiodistal center of the tooth. Further, when a clinician uses the bracket body portion of an appliance as the primary landmark, parallax is also a complicating circumstance that gives the clinician an incorrect apparent view of appliance position, as illustrated in FIG. 1H.
Notwithstanding the problems and disadvantages stated above, the concept of visual positioning of orthodontic appliances on the teeth of patients remains a technique that clinicians must use. Therefore, there remains a need for a solution to the problems of the prior art and for greater accuracy and reliability in visual appliance positioning.
A primary objective of the present invention is to alleviate the deficiencies of the prior art appliances that render inefficient and imprecise the visual positioning of orthodontic appliances on the teeth of patients. It is a particular objective of the present invention to provide an orthodontic appliance that provides a visual signal to the clinician that enhances the ability and the likelihood of achieving precise and accurate placement of the appliance on the teeth of a patient.
In accordance with the principles of the present invention, the orthodontic appliance, and particularly the portion thereof that lies against the tooth of a patient, is contoured in a way that corresponds to the profile of the tooth on which the appliance is to be positioned, so as to provide a signal that guides the clinician in the easy and precise positioning of the appliance on the tooth. It is a particular objective of the present invention to provide orthodontic appliances with tooth mounting surface thereon that are shaped to provide to the clinician who is placing the appliance on the tooth of a patient a placement signal that will facilitate the centering of the appliance on the tooth of the patient and will override erroneous signals that are caused by irregularities in the actual profile or shape of the patient""s teeth.
In accordance with the preferred embodiment of the invention, orthodontic appliances such as orthodontic brackets are provided with bases of pads that have shapes related to the frontal anatomies of the specific respective teeth to which the appliance is to be attached. The archwire support portion of the appliance is, in one embodiment, fixed relative to the pad so that the plane of the archwire passes through the FA point of the tooth when the pad is properly positioned on the tooth. In alternative embodiments, the wire support portion of the bracket is fixed to the pad, extending rigidly from the pad, so that the archwire plane intersects the tooth at a position other than through the FA point that meets some intended placement criteria offset from the FA point.
In one preferred embodiment of the invention, the archwire support portion of a bracket is fixed to a pad so that the pad can be positioned upon the mesiodistal center of the tooth by a visual centering of the tooth in a facial view with the bracket at the height of the contour of the mid-developmental lobe. Such support portions are fixed to the pad, either by being formed separate from the pad and being attached to the pad by welding, fusing or other bonding technique or by being formed integral with the pad in a molding, forging, casting, machining or other such manufacturing operation. The brackets being so formed, the support portion extends rigidly from the pad and is located on the opposite side of the pad from the mounting surface at which the pad is to be attached to a tooth. The position of the archwire support on the pad may be defined in relation to the a point on the mounting surface, thereby making it possible to locate the support by properly positioning the pad on a tooth.
In accordance with the principles of the present invention, the bases or mounting pads of the appliances are shaped to conform to the outlines or profiles of the teeth to which the bases are to attach. The profiles are preferably the silhouettes of the specific teeth when viewed from the facial side of the tooth in a lingual direction in the archwire plane. The sizes of the pads, so shaped, are preferably geometrically reduced or scaled down from the sizes of the profiles of specific teeth. The profile shapes are preferably statistically average shapes for each tooth type among the members of a population segment. The appliances having bases so shaped send to the clinician, who is mounting the appliances on the teeth of a patient, a strong visual signal, which, when received by the eye of the clinician, guides the clinician in the placement of the appliances at the visual centers of the teeth. With the bases or pads to be so located, the archwire support portions of the appliances can be either centered on the bases or offset from the centers of the bases so that they assume their intended positions on the teeth.
With the preferred embodiment of the invention, the shapes of the pads or bases of the appliances are determined by producing an outline or profile of the tooth as would be seen by the installing clinician from the facial side of the teeth. This outline is then scaled downward in size to a size that is appropriate for the appliance base or pad. The size reduction of the shapes from the that of the tooth outline to that of the finished appliance base or pad may be carried out according to a scale that differs in the horizontal and vertical directions. For example, a bracket pad may be scaled in the horizontal direction to 50% of the horizontal dimension of the tooth while being scaled in the vertical direction to 25% of the dimension of the tooth.
The appliances of the present invention and the methods of making and placing such appliances provide the advantages of more efficient and precise visual placement of the appliances on the teeth. In addition, such appliances and methods provide for a reduction in bracket adhesive failure, since the shaped pads may easily have at least a twenty percent increase in bonding area, and in some cases, much more. This increase may be provided without noticeable deterioration in esthetics by carefully enlarging the pad only in areas where the increase would be unnoticed when a ligature and archwire are present. This is accomplished while still maintaining the anatomical placement registration.
In addition, the difficulty of excess adhesive cleanup is reduced because the pads have no sharp corners, so that cleanup can be achieved with fewer discreet moves than with an orthogonal pad. Additionally, the tie wings of the brackets can be more easily made so as not to extend beyond the pad and therefore be less likely to snag on the cleanup instrument and thereby dislodge or alter the position of the appliance. Also, the likelihood of appliance drift prior to adhesive polymerization is further reduced because the ratio of the area of the pad to the mass of the assembly is greater in relation to that of the standard orthogonal pad, thereby lessening the propensity for the appliance to move due to gravity before the adhesive polymerizes.
A further advantage of the tooth-shaped pad is that the pad itself serves as a bracket identifier that is different for each tooth type and also for each quadrant, because the tooth-shaped pads carry tooth specific anatomic information that visually describes which tooth the appliance is designed for, simplifying identification of the particular appliance.
Patient hygiene and iatrogenic decalcification are improved with the tooth-shaped pads because the bracket tie wings need not exceed the perimeter of the pads, and therefore the patient is able to access this area with a toothbrush to minimize the decalcification commonly seen at the gingival edge of the pad. Additionally, the pads may be designed to cover the gingival areas where decalcification is common.
The quality of pad fit with respect to tooth curvatures is further increased with the pads shaped according to the present invention, because, while the pad of a standardized bracket is unlikely to fit any tooth perfectly, the tooth-shaped pads have less in the way of corners than do orthogonal pads, so teetering across the diagonal corners of the orthogonal pads is lessened.
The present invention is particularly advantageous in the application of appliances to the maxillary teeth, although certain features of the invention provide advantages in the application of appliances to mandibular teeth.
These and other objectives and advantages of the present invention will be more readily apparent from the following detailed description of the drawings of the preferred embodiment of the invention, in which: